Vented shaft seal



y 27, 1952 H. N. HOFFMAN 2,598,381

VENTED SHAFT SEAL Filed July 6, 1949 lnve'ntcr Herbert'N. Hoffrnan,

His Attorney.

Patented May 27, 1952 VENTED SHAFT SEAL Herbert N. Hoffman, Wakefield,Mass., assignor to General Electric Company, a corporation of New YorkApplication July 6, 1949, Serial N0. 103,208

8 Claims.

This invention relates to scaling arrangements for rotating shaftssupported in bearings disposed in substantially sealed housings. Whilenot limited thereto, the invention has particular utility in connectionwith preventing oil leakage from the shaft bearings of high speed primemovers such as steam turbines.

In the case of a machine having a high speed shaft carried in bearingsdisposed in substantially sealed bearing housings, it is frequentlyfound that rotation of the shaft and associated members results in abuilding up of pressure inside the bearing housing, which has a tendencyto force oil out through the shaft seals. This problem has beenparticularly troublesome in connection with small high speed turbinesrunning at speeds up to 10,000 R. P. M. An important part of thesolution to this oil leakage lies in providing a vent to relieve theinternal pressure which would otherwise build up inside the bearinghousing. However, providing a suitable vent, arranged so that oil or oilvapor will not escape therefrom, usually proves to be a very difficultproblem:

Accordingly, itis an object of the present invention to provide a shaftseal structure which incorporates an unusually effective ventingarrangement for the interior of the bearing housing, and at the sametime positively resists the leakageof oil along the shaft from thebearing housing.

More specifically, the purpose of the invention is to provide' a shaftseal arrangement which performs the following functions:

1. Effects positive venting of the bearing housing at the place whereventing is needed most, namely immediately adjacent the shaft andcommunicating with the space adjacent the inside wall of thecasing.

2. Produces a centrifuging action on any oilair Vapor mixture whichtriesto leave the bearing housing, so that the oil particles are separatedfrom theair. p

3. Produces a positive pumping action on the air, forcing it 'to theexterior of the bearing housing.

4. Produces a positive pumping action on the oil, forcing it back intothe bearing housing.

With the present invention, all these functions are performedsimultaneously by, extremely simple structural means requiring nosubstantial increase in dimensions of the bearing housing, either in anaxial orradial direction. Other objects'and advantages will be apparentfrom the following description taken in connection with the accompanyingdrawings, in which Fig. l is a sectional view of a sealed bearinghousing structure employing two different forms of the invention at therespective ends of the housing; Fig. 2 is a detail sectional Viewshowing a third modification; and Fig; 3 is a sectional view of a stillfurther modification.

Referring now more specifically to Fig. 1, the rotating shaft l issupported in a plain journal bearing 2, which may be of any suitabletype. It will be obvious that the invention is equally applicable toarrangements employing various types of anti-friction bearings. Thedetails of the bearing employed are not material to an understanding ofthe present invention and therefore are not described further here. Itmay be noted however, that lubricating oil is supplied by a suitableconduit 3 to the rubbing surfaces of the bearing 2 through passagesprovided in the housing 4. Although not shown clearly in the drawings,it will be understood by those skilled in the art that, in order tofacilitate assembly, the housing 4 is actually split on a horizontalplane through the center line of shaft I, the two halves being securedtogether by any suitable fastening devices. The bearing housing 4 issupported in any suitable manner, for instance by a bracket 5 secured tothe casing of a machine.

The lower half of housing '4 forms a sump 6 in which collects the spentoil from hearing 2, and from which this oil is returned to thelubrication system, as by means of a drain conduit 1. It will of coursebe appreciated that the invention is also applicable to bearings of thetype in which oiling rings or equivalent devices are carried on theshaft and have a portion dipping into the oil in reservoir 6, so thatthe rotation of the shaft causes the oil to b carried up onto the top ofthe shaft, instead of being supplied under pressure through theconduit'3.

Surrounding the shaft l at either end of the bearing housing 4 are theventing and sealing devices which are the subject of the presentinvention. The sealing structure at the left-hand end of the bearinghousing comprises a cylindrical sealing member 8 which is shrunk,pressed, or otherwise firmly secured to the shaft I so that there is nofluid leakage path between the member 8 and the shaft I. provided withan annular recess 9 the outer wall of which tapers, with its majordiameter at the right-hand end and located within the bearing housing,While the exterior end is of substan- The member 8 is tially smallerdiameter and located exterior of the bearing housing. The interior endof the sealing member 8 is provided with a plurality of radiallyextending circumferentially spaced holes Hi. It will be obvious from aconsideration of the drawing that these passages I communicate directlywith the space inside the bearing housing immediately adjacent theinterior wall ofrth'e housing. At the exterior side of the bearinghousing, the end portion of sealing cylinder 8 is provided with aradially extending flange II having a plurality of circumferentiallyspaced radially extending holes [2.

It is to be noted particularly that the annular chamber 9 is of a rathersubstantial axial length and of sufficient volume to form a centrifugechamber in which the oil and air mixture from the interior of thebearing'housin'g is caused to whirl at shaft speed. It will also beobserved that the surface of the tapered chamber 9 experiences agradualchange in diameter without any discontinuities in the smoothtaper from the menl iemete t6 he-lar i 'Also th passages 12.aresubstantially longer in radial direction than the passages] 0,;thatisj, they discharge at a substantially greater radius from thecenter of the shaft than the inlets to the passages [0. Although; itcannot ,be readily ascertained from the drawing, it istobe noted thatthe passages l0 areof such a cros s section size and number as toprovide an aggregate flow path of substantially greater agreathlanthatprovided bythe passages 52, For in tance the holes l0, l2 may be ofthe same diameterfbut there may be eight of the holes lilfwh e therearea smaller number, for instance 4 x oftheholes #2. The reason for thesedesign features will be" seen from the following descriptipn'of lthemethod of operation.

in operation the sealing cylinder member 8 rotates withthe shaft I andany pressurewhich tendsfto build up within the bearing housing 4 causesa'LfiOwIof' airIand entrained oil particles radi inward through thepassages 10 and into p chtr i'fugechamberfl'. It will be obvious thatinfltlire 'proce's's 'of. passing inwardly through th raaiai'passag'es,1 n, the air-0'11 mixture'isfgi'vfn ajrctau nm velocity equalor'substaat anyjequ l' to that of the cylinder member 8; "Thus the fiiiiWithinthe chamber 9 is caused to whirlwitha velocity equalor'substantially equal to thatpf the shaftv andcylirider 8. Theresulting;centrifugal effect, on the oil-air mixthe" avier oil particlesto coalesce I outwardly so asto strike the taperingjouteisurface'of"ch'amber 9., The air, of courseremains freeto flow to the leftthrough the space}? and outjthe radial pumping passages i2. 'Dueftothe;fa'cftjthat passages l2 discharge at a materially gre'ater radius thanthe intake to the passages 'l0, there is a positive net centrifugalpumping action tending to induce aflow of air fromtheinside of thebearing housing out through thepassages H), 9, l2 as indicated by theair flow arrowsjinFig l. On the other hand, the heavier oilparticlesarethrown against the tapering inner surface'pf the chamber 9, after whichthe'cdntinuing effect of centrifugal force'makes the oil particles flowalong the outwardly tapering surface'to the right until they aredischarged backthroughthe passages [0 to the interior of the bearinghousing.

The reason for makingthe aggregate effective area of the passages I0substantially larger than that of the passages 12 i's so the oil canlfiow back into the bearing 'housingfthrough the same the n emen fi x refieli ftsfij re ing or completelyeliminating the, problem of oil set ofpassages which leads the air-oil mixture from the bearing housing intothe centrifuge chamber 9. Since the passages l2 handleonly air, they maybe of smaller effective area.

The further modification shown in Fig. 3 is identical to that in Fig. 2,except that the bore of the sealing member 8 is not tapered but has alarge, diameter centrifuge chamber l8, the central part of whichcommunicates with a comparatively small annular passage 59, as will beobvious from Fig. 3. With this arrangement, a strong vortex whirl isproduced in the centrifuge chamber I8 effecting substantially completeseparation of oil from air. The oil is of course pumped back into thehousing through the radial passages 10. The comparatively pure air atthe core of the vortex in chamber I8 is pumped out through the passage19. It will of course be understood that the centrifuge chamber I0 is ofsufiicient axial length that the oil will have been quite thoroughlyseparated from th e air;b ef ore the mixture gets as far as the entranceto the pas a e The arrangement o f; Fig. 3 has beenjoundto be not quiteas effective. as thatofFigg 1 and where I the centrifuge chamber is ofcohsiderably greater axial length and-the tapered su I th bor more p sitvelvin 'i res ee er returned to the inner set of holes llh However. thearrangement 'of Fig 3 may-v be found somea easier a u a ture nd. i es'ae ib results, at least in some applications 7 It will be seenfromtheabovethat-the invention provides not just a passiveventIarrangement for pe m t nah .P essure eflr d... side the bearingousi s q es a e m tmp' phera but on the other hand effects afdynamicvent in in which rin he ou P s t pumped to the exterior so that-thepressure-inside the bearing housing may be somewhatbelqw that of thesurrounding atmosphere. This of course efiectivelyresists the tendencyof thepil or oilvapor in the housing.to leakoutwardly through the shaftseal In additionfto ,very important venting func nftheginyention effectsa strong centrifuging tending .to s p rat the entrained oil from the,air which is pumped out of the 'bearing 'houslng And finally, .theoer}. trifuged oil is positively pumpedby centrifugal force back intothe housimg.

It will therefore be seen that, by Verysim'p'le structural means, an.arran gement is pifovided which vents the housing,or even reduces the interior pressure below th'at of the shrroundihgla'tmosphere, 'separatesoil from the air've'nted from the housing, and positively pumps the air.out of the housing and the oil back in- Use of the invention onhighspeedmachi'n'es such as small steam turbines'operatingfintheneighborhood of 10,000 R; P.-M. has

leakage.

The above description of I the features to whiich this inventionparticularly relates has not in-, cluded the oil sealing arrangementprovided be tween the walls ofthe housing and the outer surface of thesealing cylinder-0.; It will ,of; course be obvious that there isnecessarily some slightclearance between h te faceef-c drer B and thecircularvpening i he housi -l: s ncun at the left side of Fig. 1, thewall ofghousi lhg g i provided with an annular recess 1 3 conce tric;with the shaft and forming annularlands 13%;

bi hf m- Psec earanc s:w hthecut surface of cylinder 8. The lowerportion of groove l3 communicates by way of a passage M with the oilsump 6. It will be apparentthat any oil leaking through the clearancewith land. l3b will collect in the recess I3 and be drained back intothe sump 6 by way of the passage M.

It will also be observed that the land l3b has a circumferential surfacesomewhat larger 'in diameter than the land l3a. The former forms a closeclearance with a cylindrical surface 8a. of the sealing cylinder 8,while the latter forms a close clearance with a second cylindricalsurface 8b. The cylindrical surfaces 8a, 8b are joined by a narrow,radially extending annular surface 80. Centrifugal force will make itvery diflicult for any oil particles to progress from the larger radiusof the clearance space between'8'a, l3b to the smaller radius of theclearance space between 8b, [3a. Furthermore, the radially extendingsurface 80 will serve as an "oil slinger tending to throw into therecess [3 any oil particles which may contact the surface 8b. It will ofcourse be apparent that the surface 8b might be made with a slighttaper, roughly parallel to the taper of the outer surface of chamber 9so that any oil contacting the surface 8b would tend to progress bycentrifugal force to the right until it was thrown off by the slingersurface 80.

It is to be understood that the sealing arrangement provided between theexternal surface of the O sealing member 8 and the adjacent wall of thehousing 4 may be of any suitable type. An alternate form is shown at theright-hand side of Fig. 1. Here the sealing cylinder member 8 isidentical to that shown at the left-hand side of Fig. 1, except that theexternal surface is shaped to provide a somewhat different sealingarrangement with the housing. Here the housing forms axially spacedcircumferential lands l6a, "5b, which form close radial clearances withthe outer cylindrical surface [5a. of the sealing cylinder member 8. Thesurface I5a is interrupted by a circumferential ridge I! which serves asan oil slinger to prevent oil particles from progressing along thesurface [5a to the right. It will be obvious that the slinger I1 causesoil particles to be thrown into the drain recess [6 instead ofprogressing further to the right through the clearance between I617,I511.

Fig. 2 shows a still further modification of the oil seal between thesealing cylinder member 8 and the annular lands l3a, I 3b. It will beseen that here again the sealing cylinder member 8 is identical withthat shown at the left-hand side of Fig. 1, except for the configurationof the outer surface. The outer cylindrical surface lid is provided witha circumferential groove Be, the radially extending sidewalls of whichserve as slingers to throw off oil particles into the collecting chamber13, instead of permitting them to travel through the clearance with landl3a.

All these sealing arrangements described for preventing leakage of oilaround the outside of the sealing cylinder 8 are perfectly feasible, al-

though that shown at the left-hand side of Fig. 1 has been found to bemost'eflfective, that at the right-hand side of Fig. 1 next best, whilethat shown in Fig. 2 is the least effective of the three illustrated. Itshould be noted however that a great many other types of shaft seal, forinstance many types of known rubbing shaft seal devices may be employed.

The invention has another advantage when used as shown in the drawing,as follows. It will be noted that the radial clearances between thecasing lands l3a, i311 and the cylindricalsurfaces 8b, 8a. (and thecorresponding clearances in the other modifications illustrated) havebeen somewhat exaggerated in the drawings for purposes of clearerillustration. Actually the clearances are made as small as manufacturingconvenience will permit. Leakage of oil outward through these clearancesis resisted by the stream of atmospheric air flowing inwardly, this airflow being induced by the sub-ambient pressure developed inside thehousing as described above. Thus the special sealing member 8 servesindirectly to prevent oil leakage around the outside of it, as well asthrough it. 7

It will be obvious that many changes and modifications in variousmechanical details may be made, and I intend to cover by the appendedclaims all such modifications as fall within the true spirit and scopeof the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In a venting arrangement for a substantially sealed housing having aliquid inside with a high speed shaft projecting through a wall thereof,the combination of a substantially cylindrical sealing member on theshaft, said sealing member and, shaft defining an axially extendingcentrifuge chamber of annular cross-section coaxial with the shaft andsmoothly tapering from a smaller diameter at the exterior side of thesealed housing to a larger diameter adjacent the inner surface of thehousing wall, the interior end of the sealing member defining firstradially extending passages communicating with the major' diameter ofthe centrifuge chamber, the exterior end of the sealing member definingsecond radially extending passages communicating with the minor diameterof the chamber and discharging into the ambient atmosphere atasubstantially greater radius than the inlet to'said first passages fromthe interior of the housing, and sealing means for preventing leakage offluid between the housing wall and the surface of said sealing memberintermediate said first and second passages, whereby centrifugal forcecauses liquid particles in thecentrifuge chamber to be thrown onto saidtapered surface and returned into the housing through thefirst-mentioned passages while gases in the centrifuge chamber arepositively pumped out through the second-mentioned passages to induce aflow of fluids through said first passages into the centrifuge chamberand thereby reduce the pressure inside the sealed housing.

2. In a vented fiuid seal assembly for a highspeed rotor having aportion disposed through an opening in a wall of a substantially sealedhousing, the combination of rotor portions located adjacent the openingin the housing wall and having an interior centrifuge chamber with anouter wall of circular cross-section coaxial with the rotor and smoothlytapering axially from a minor diameter adjacent the exterior side of thesealed housing to a major diameter adjacent the interior side of thehousing, said rotor defining a first set of radially extending passagescommunicating with the major trifuge chamber and with the space insidethe sealed housing, said rotor also defining a second set of radiallyextending passages communicating with the minor diameter of thecentrifuge chamber and discharging exteriorly of the sealed housing, thedischarge ends of said second set of passages being at a substantiallygreater radius than the inlets to said first set of passages, and meansfor preventing'leakage of fluid from inside the housing through theclearance space'bediameter of the cen-.

tween the outer surface of'tl'leirotorand' the adjacent surfaces 6f thehousing, 'wherebyc'en trifugal rereejiaiis'esliquid particles threatrifug'e chamber' to b'e-thrown outwardly onto the tapered wallthereof-and"pumped-back into the housing through said first-mentioned"set of passages while gaseous components of the mixture in thecentrifuge chamber are positively pumped out through thesecond-mentioned set of passages to reduce the pressure insidethe'sealed housing;

3. In a vented liquid seal assembly-fora rotary shaft disposed through awall of a substantially sealed housing, the combination of a-cylindricalsealing member on the shaft" and-*defining-an axially-extending taperedannular ehambersurrounding-the shaft with a major-diameter at theinterior side nearer the bearing and a miner diameter toward's'th'eexterior "ofthe' bearing housing, the interior end of said memberdefining first radially extending passages communicating with the majordiameter of said chamber and the exterior end of said member definingsecond radially extending passages communicating with the minor diameterof said chamber, and sealing means for preventing leakage of fluidthrough-the clearance space between the housing and exterior surface ofsaid seal member intermediate said first and second radial passages,whereby gases inside the housing are vented to atmosphere throughthesecond passages while liquid particles 3 are centrifug'ally separatedfrom the gases and returned to the housing through the first radialpassages.

4. A vented shaft seal member comprising a cylindrical body with acentral bore including first and second axially spaced end bore portionsadapted to engage a shaft in fluid sealing relation therewith and anintermediate bore portion with a smoothly tapered W'all extendingaxially from a minor diameter adjacent the first en'd bore portion to amajor diameter adjacent the second end bore portion, the first endportion of the member defining a plurality of radially extendingpassages communicating with said intermediate bore portion at its minordiameter, said second end portion defining a second set of radiallyextending passages communicating with said intermediate bore portion atits major diameter, the outer surface of said'member inter mediate thefirst and second sets of radial passages being shaped to form at leastone radially extending liquid slinger surface for resisting the passageof liquid axially along the outer surface of the member, the radiallyouter portions of the first setof passages being-at a substantiallygreater radius from'the center of rotation than the radially outerportions of the second set "of passages, whereby'hi'gh speedrotationofthe sealing member with an associated shaft wwill efiect apositive centrifugal-pumping action tendingto draw fluid radially inwardthrough the second set of passages, liquid and gaseous components beingcentrifugally separated linis'aid intermediate bore portion, withthegaseous fcom= ponents being pumped out through the first set ofpassages while liquidcomponentstravel axially 5 along the surface of thetapered bore portionand are expelled radially outward through the.second set of passages.

5. In a venting arrangement for a substantially sealed housing having aliquid inside and a high speed shaft projecting through a wall thereof,the combination of a substantiallyzcylindrical sealing'memb'er on theshaft, the sealing member and shaft cooperating to define an axially"extending centrifuge chamber of annular "cross;

section coaxial with'the 'sh'aftand including a 'larger'diameter portionat the end of the sealing-member'adjacent theinterior of'the housing.andz'a'da'pted to form a liquid separating chamber and a second smallerdiameter portion communicating with the liquid separatingchamher andextending axially towards th'e'exterior side of the sealing member, theinterior end of the sealing member defining first radially extendingpassages communicating with the outer circumferential portion of saidliquid separating chamber and the space'within the housing; the exteriorend of the sealing member defining second radially extending passagescommunieating with the adjacent end of said small diameter portion anddischarging into 'thear'nbie'nt atmosphere at a substantiallyvgreaterradius than the radially outerp'ortion of said first passage, andmeansfor preventing leakage of fluid between 'thehousing wall and theouter circumferential surface of the sealing member intermediate thefirst and second passages, whereby centrifugal force causes liquidparticles in the liquid separating chamber to be thrown outwardlyontothe circumferential walls of the chamber and returned to the housingthrough the first-mentioned passages, while gases at the central portionof the centrifuge chamber are drawn or through the smaller diameterchamber portion and positively pumped out through the secondmenticnedpassages to reduce the pressure inside the sealed housing.

6. In a vented fluid seal assembly for a high speed rotor having aportion disposed through an opening in a wall of a substantially sealedhousing,'the combination of rotor portions located adjacent the openingin the'hou'sing wall and forming an interior centrifuge chamber with anouter wall of circular cross-section coaxial with the shaft andcommunicating with a smaller diameter coaxial wall forming an' axiallyextending passage, the rotor having a first set of radially extendingpassages communicating with the outer portion of said centrifuge chamberand with the space inside the sealed housing,- the rotor also defining asecond set of radially extending passages communicating with the smallerdiameter axial passage and discharging to the exterior of the sealedhousing,the discharge ends of said second set of passages being at asubstantially greater radius than the radially outer portions of saidfirst set of passages, and means for resisting leakage of fluid frominside the'housing through the clearance space between the outercircumferential surface of the rotor and the adjacent portions of thehousing, whereby centrifugal force causes liquid particles inthe'centrifuge chamber to be thrown outwardly and pumped back into thehousing through the firstementioned set of passages while gaseouscomponents of the mixture in the centrifugechamber are drawn off throughthe axially extending passage and positively pumped-out through thesecond set 'of passages to reduce the pressure inside the sealed housingand thereby reduce the tendency of fluids inside the housing to leakoutwardly through said leakage resisting means.

7. A vented fluid seal assembly in accordance with claim 6 in which theouter wall of the centrifuge chamber is of substantially constantdiameter and the outer wall of the axially extending passage for thedischarge of gases is likewise of .a diameter which is constant butsubstantially smaller .than that of the centrifuge chamber; thecylindrical surfaces of I the centri- 9 fuge chamber and axial passagebeing connected by a substantially radially extending annular surfacewhich resists the entry of liquid particles into the axial passage.

8. In a vented fluid seal assembly for a high speed rotor having aportion disposed through an opening in a wall with a gaseous medium atone side thereof and gases and liquids at the other side thereof, thecombination of rotor portions located adjacent the opening in the walland defining an interior centrifugechamber the outer wall of which is ofcircular cross section coaxial with the rotor and communicating with asmaller diameter cylindrical wall portion forming an axially extendingpassage, the rotor having a first set of radially extending passagescommunicating with the outer portion of said centrifuge chamber and withthe space at the side of the wall containing both liquid and gaseousmedium, the rotor also defining a second set of radially extendingpassages communicating with the smaller diameter axial passage eat alocation spaced from the centrifuge chamber and discharging at theopposite side of said wall, the

discharge ends of said second set of passages being at a substantiallygreater radius than the radially outer portions of said first set ofpassages, and means for resisting leakage of fluids from one side of thewall to the other through the clearance space formed between the outercircumferential surface of the rotor and the surrounding portions of thewall, whereby centrifugal force causes liquid particles in thecentrifuge chamber to be thrown outwardly and pumped through said firstset of passages while gaseous components of the mixture in thecentrifuge chamber are drawn off through said axially extending passageand pumped out through the second set of passages.

HERBERT N. HOFFMAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

